/* * random.c -- A strong random number generator * * Copyright Matt Mackall <mpm@selenic.com>, 2003, 2004, 2005 * * Copyright Theodore Ts'o, 1994, 1995, 1996, 1997, 1998, 1999. All * rights reserved. * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * 1. Redistributions of source code must retain the above copyright * notice, and the entire permission notice in its entirety, * including the disclaimer of warranties. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in the * documentation and/or other materials provided with the distribution. * 3. The name of the author may not be used to endorse or promote * products derived from this software without specific prior * written permission. * * ALTERNATIVELY, this product may be distributed under the terms of * the GNU General Public License, in which case the provisions of the GPL are * required INSTEAD OF the above restrictions. (This clause is * necessary due to a potential bad interaction between the GPL and * the restrictions contained in a BSD-style copyright.) * * THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESS OR IMPLIED * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE, ALL OF * WHICH ARE HEREBY DISCLAIMED. IN NO EVENT SHALL THE AUTHOR BE * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF * LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE * USE OF THIS SOFTWARE, EVEN IF NOT ADVISED OF THE POSSIBILITY OF SUCH * DAMAGE. *//* * (now, with legal B.S. out of the way.....) * * This routine gathers environmental noise from device drivers, etc., * and returns good random numbers, suitable for cryptographic use. * Besides the obvious cryptographic uses, these numbers are also good * for seeding TCP sequence numbers, and other places where it is * desirable to have numbers which are not only random, but hard to * predict by an attacker. * * Theory of operation * =================== * * Computers are very predictable devices. Hence it is extremely hard * to produce truly random numbers on a computer --- as opposed to * pseudo-random numbers, which can easily generated by using a * algorithm. Unfortunately, it is very easy for attackers to guess * the sequence of pseudo-random number generators, and for some * applications this is not acceptable. So instead, we must try to * gather "environmental noise" from the computer's environment, which * must be hard for outside attackers to observe, and use that to * generate random numbers. In a Unix environment, this is best done * from inside the kernel. * * Sources of randomness from the environment include inter-keyboard * timings, inter-interrupt timings from some interrupts, and other * events which are both (a) non-deterministic and (b) hard for an * outside observer to measure. Randomness from these sources are * added to an "entropy pool", which is mixed using a CRC-like function. * This is not cryptographically strong, but it is adequate assuming * the randomness is not chosen maliciously, and it is fast enough that * the overhead of doing it on every interrupt is very reasonable. * As random bytes are mixed into the entropy pool, the routines keep * an *estimate* of how many bits of randomness have been stored into * the random number generator's internal state. * * When random bytes are desired, they are obtained by taking the SHA * hash of the contents of the "entropy pool". The SHA hash avoids * exposing the internal state of the entropy pool. It is believed to * be computationally infeasible to derive any useful information * about the input of SHA from its output. Even if it is possible to * analyze SHA in some clever way, as long as the amount of data * returned from the generator is less than the inherent entropy in * the pool, the output data is totally unpredictable. For this * reason, the routine decreases its internal estimate of how many * bits of "true randomness" are contained in the entropy pool as it * outputs random numbers. * * If this estimate goes to zero, the routine can still generate * random numbers; however, an attacker may (at least in theory) be * able to infer the future output of the generator from prior * outputs. This requires successful cryptanalysis of SHA, which is * not believed to be feasible, but there is a remote possibility. * Nonetheless, these numbers should be useful for the vast majority * of purposes. * * Exported interfaces ---- output * =============================== * * There are three exported interfaces; the first is one designed to * be used from within the kernel: * * void get_random_bytes(void *buf, int nbytes); * * This interface will return the requested number of random bytes, * and place it in the requested buffer. * * The two other interfaces are two character devices /dev/random and * /dev/urandom. /dev/random is suitable for use when very high * quality randomness is desired (for example, for key generation or * one-time pads), as it will only return a maximum of the number of * bits of randomness (as estimated by the random number generator) * contained in the entropy pool. * * The /dev/urandom device does not have this limit, and will return * as many bytes as are requested. As more and more random bytes are * requested without giving time for the entropy pool to recharge, * this will result in random numbers that are merely cryptographically * strong. For many applications, however, this is acceptable. * * Exported interfaces ---- input * ============================== * * The current exported interfaces for gathering environmental noise * from the devices are: * * void add_input_randomness(unsigned int type, unsigned int code, * unsigned int value); * void add_interrupt_randomness(int irq); * * add_input_randomness() uses the input layer interrupt timing, as well as * the event type information from the hardware. * * add_interrupt_randomness() uses the inter-interrupt timing as random * inputs to the entropy pool. Note that not all interrupts are good * sources of randomness! For example, the timer interrupts is not a * good choice, because the periodicity of the interrupts is too * regular, and hence predictable to an attacker. Disk interrupts are * a better measure, since the timing of the disk interrupts are more * unpredictable. * * All of these routines try to estimate how many bits of randomness a * particular randomness source. They do this by keeping track of the * first and second order deltas of the event timings. * * Ensuring unpredictability at system startup * ============================================ * * When any operating system starts up, it will go through a sequence * of actions that are fairly predictable by an adversary, especially * if the start-up does not involve interaction with a human operator. * This reduces the actual number of bits of unpredictability in the * entropy pool below the value in entropy_count. In order to * counteract this effect, it helps to carry information in the * entropy pool across shut-downs and start-ups. To do this, put the * following lines an appropriate script which is run during the boot * sequence: * * echo "Initializing random number generator..." * random_seed=/var/run/random-seed * # Carry a random seed from start-up to start-up * # Load and then save the whole entropy pool * if [ -f $random_seed ]; then * cat $random_seed >/dev/urandom * else * touch $random_seed * fi * chmod 600 $random_seed * dd if=/dev/urandom of=$random_seed count=1 bs=512 * * and the following lines in an appropriate script which is run as * the system is shutdown: * * # Carry a random seed from shut-down to start-up * # Save the whole entropy pool * echo "Saving random seed..." * random_seed=/var/run/random-seed * touch $random_seed * chmod 600 $random_seed * dd if=/dev/urandom of=$random_seed count=1 bs=512 * * For example, on most modern systems using the System V init * scripts, such code fragments would be found in * /etc/rc.d/init.d/random. On older Linux systems, the correct script * location might be in /etc/rcb.d/rc.local or /etc/rc.d/rc.0. * * Effectively, these commands cause the contents of the entropy pool * to be saved at shut-down time and reloaded into the entropy pool at * start-up. (The 'dd' in the addition to the bootup script is to * make sure that /etc/random-seed is different for every start-up, * even if the system crashes without executing rc.0.) Even with * complete knowledge of the start-up activities, predicting the state * of the entropy pool requires knowledge of the previous history of * the system. * * Configuring the /dev/random driver under Linux * ============================================== * * The /dev/random driver under Linux uses minor numbers 8 and 9 of * the /dev/mem major number (#1). So if your system does not have * /dev/random and /dev/urandom created already, they can be created * by using the commands: * * mknod /dev/random c 1 8 * mknod /dev/urandom c 1 9 * * Acknowledgements: * ================= * * Ideas for constructing this random number generator were derived * from Pretty Good Privacy's random number generator, and from private * discussions with Phil Karn. Colin Plumb provided a faster random * number generator, which speed up the mixing function of the entropy * pool, taken from PGPfone. Dale Worley has also contributed many * useful ideas and suggestions to improve this driver. * * Any flaws in the design are solely my responsibility, and should * not be attributed to the Phil, Colin, or any of authors of PGP. * * Further background information on this topic may be obtained from * RFC 1750, "Randomness Recommendations for Security", by Donald * Eastlake, Steve Crocker, and Jeff Schiller. */#include<linux/utsname.h>#include<linux/module.h>#include<linux/kernel.h>#include<linux/major.h>#include<linux/string.h>#include<linux/fcntl.h>#include<linux/slab.h>#include<linux/random.h>#include<linux/poll.h>#include<linux/init.h>#include<linux/fs.h>#include<linux/genhd.h>#include<linux/interrupt.h>#include<linux/mm.h>#include<linux/spinlock.h>#include<linux/percpu.h>#include<linux/cryptohash.h>#include<linux/fips.h>#ifdef CONFIG_GENERIC_HARDIRQS# include <linux/irq.h>#endif#include<asm/processor.h>#include<asm/uaccess.h>#include<asm/irq.h>#include<asm/io.h>/* * Configuration information */#define INPUT_POOL_WORDS 128#define OUTPUT_POOL_WORDS 32#define SEC_XFER_SIZE 512/* * The minimum number of bits of entropy before we wake up a read on * /dev/random. Should be enough to do a significant reseed. */staticintrandom_read_wakeup_thresh=64;/* * If the entropy count falls under this number of bits, then we * should wake up processes which are selecting or polling on write * access to /dev/random. */staticintrandom_write_wakeup_thresh=128;/* * When the input pool goes over trickle_thresh, start dropping most * samples to avoid wasting CPU time and reduce lock contention. */staticinttrickle_thresh__read_mostly=INPUT_POOL_WORDS*28;staticDEFINE_PER_CPU(int,trickle_count);/* * A pool of size .poolwords is stirred with a primitive polynomial * of degree .poolwords over GF(2). The taps for various sizes are * defined below. They are chosen to be evenly spaced (minimum RMS * distance from evenly spaced; the numbers in the comments are a * scaled squared error sum) except for the last tap, which is 1 to * get the twisting happening as fast as possible. */staticstructpoolinfo{intpoolwords;inttap1,tap2,tap3,tap4,tap5;}poolinfo_table[]={/* x^128 + x^103 + x^76 + x^51 +x^25 + x + 1 -- 105 */{128,103,76,51,25,1},/* x^32 + x^26 + x^20 + x^14 + x^7 + x + 1 -- 15 */{32,26,20,14,7,1},#if 0 /* x^2048 + x^1638 + x^1231 + x^819 + x^411 + x + 1 -- 115 */ { 2048, 1638, 1231, 819, 411, 1 }, /* x^1024 + x^817 + x^615 + x^412 + x^204 + x + 1 -- 290 */ { 1024, 817, 615, 412, 204, 1 }, /* x^1024 + x^819 + x^616 + x^410 + x^207 + x^2 + 1 -- 115 */ { 1024, 819, 616, 410, 207, 2 }, /* x^512 + x^411 + x^308 + x^208 + x^104 + x + 1 -- 225 */ { 512, 411, 308, 208, 104, 1 }, /* x^512 + x^409 + x^307 + x^206 + x^102 + x^2 + 1 -- 95 */ { 512, 409, 307, 206, 102, 2 }, /* x^512 + x^409 + x^309 + x^205 + x^103 + x^2 + 1 -- 95 */ { 512, 409, 309, 205, 103, 2 }, /* x^256 + x^205 + x^155 + x^101 + x^52 + x + 1 -- 125 */ { 256, 205, 155, 101, 52, 1 }, /* x^128 + x^103 + x^78 + x^51 + x^27 + x^2 + 1 -- 70 */ { 128, 103, 78, 51, 27, 2 }, /* x^64 + x^52 + x^39 + x^26 + x^14 + x + 1 -- 15 */ { 64, 52, 39, 26, 14, 1 },#endif};#define POOLBITS poolwords*32#define POOLBYTES poolwords*4/* * For the purposes of better mixing, we use the CRC-32 polynomial as * well to make a twisted Generalized Feedback Shift Reigster * * (See M. Matsumoto & Y. Kurita, 1992. Twisted GFSR generators. ACM * Transactions on Modeling and Computer Simulation 2(3):179-194. * Also see M. Matsumoto & Y. Kurita, 1994. Twisted GFSR generators * II. ACM Transactions on Mdeling and Computer Simulation 4:254-266) * * Thanks to Colin Plumb for suggesting this. * * We have not analyzed the resultant polynomial to prove it primitive; * in fact it almost certainly isn't. Nonetheless, the irreducible factors * of a random large-degree polynomial over GF(2) are more than large enough * that periodicity is not a concern. * * The input hash is much less sensitive than the output hash. All * that we want of it is that it be a good non-cryptographic hash; * i.e. it not produce collisions when fed "random" data of the sort * we expect to see. As long as the pool state differs for different * inputs, we have preserved the input entropy and done a good job. * The fact that an intelligent attacker can construct inputs that * will produce controlled alterations to the pool's state is not * important because we don't consider such inputs to contribute any * randomness. The only property we need with respect to them is that * the attacker can't increase his/her knowledge of the pool's state. * Since all additions are reversible (knowing the final state and the * input, you can reconstruct the initial state), if an attacker has * any uncertainty about the initial state, he/she can only shuffle * that uncertainty about, but never cause any collisions (which would * decrease the uncertainty). * * The chosen system lets the state of the pool be (essentially) the input * modulo the generator polymnomial. Now, for random primitive polynomials, * this is a universal class of hash functions, meaning that the chance * of a collision is limited by the attacker's knowledge of the generator * polynomail, so if it is chosen at random, an attacker can never force * a collision. Here, we use a fixed polynomial, but we *can* assume that * ###--> it is unknown to the processes generating the input entropy. <-### * Because of this important property, this is a good, collision-resistant * hash; hash collisions will occur no more often than chance. *//* * Static global variables */staticDECLARE_WAIT_QUEUE_HEAD(random_read_wait);staticDECLARE_WAIT_QUEUE_HEAD(random_write_wait);staticstructfasync_struct*fasync;#if 0static int debug;module_param(debug, bool, 0644);#define DEBUG_ENT(fmt, arg...) do { \ if (debug) \printk(KERN_DEBUG "random %04d %04d %04d: " \fmt,\input_pool.entropy_count,\blocking_pool.entropy_count,\nonblocking_pool.entropy_count,\ ## arg); } while (0)#else#define DEBUG_ENT(fmt, arg...) do {} while (0)#endif/********************************************************************** * * OS independent entropy store. Here are the functions which handle * storing entropy in an entropy pool. * **********************************************************************/structentropy_store;structentropy_store{/* read-only data: */structpoolinfo*poolinfo;__u32*pool;constchar*name;intlimit;structentropy_store*pull;/* read-write data: */spinlock_tlock;unsignedadd_ptr;intentropy_count;intinput_rotate;__u8*last_data;};static__u32input_pool_data[INPUT_POOL_WORDS];static__u32blocking_pool_data[OUTPUT_POOL_WORDS];static__u32nonblocking_pool_data[OUTPUT_POOL_WORDS];staticstructentropy_storeinput_pool={.poolinfo=&poolinfo_table[0],.name="input",.limit=1,.lock=__SPIN_LOCK_UNLOCKED(&input_pool.lock),.pool=input_pool_data};staticstructentropy_storeblocking_pool={.poolinfo=&poolinfo_table[1],.name="blocking",.limit=1,.pull=&input_pool,.lock=__SPIN_LOCK_UNLOCKED(&blocking_pool.lock),.pool=blocking_pool_data};staticstructentropy_storenonblocking_pool={.poolinfo=&poolinfo_table[1],.name="nonblocking",.pull=&input_pool,.lock=__SPIN_LOCK_UNLOCKED(&nonblocking_pool.lock),.pool=nonblocking_pool_data};/* * This function adds bytes into the entropy "pool". It does not * update the entropy estimate. The caller should call * credit_entropy_bits if this is appropriate. * * The pool is stirred with a primitive polynomial of the appropriate * degree, and then twisted. We twist by three bits at a time because * it's cheap to do so and helps slightly in the expected case where * the entropy is concentrated in the low-order bits. */staticvoidmix_pool_bytes_extract(structentropy_store*r,constvoid*in,intnbytes,__u8out[64]){static__u32consttwist_table[8]={0x00000000,0x3b6e20c8,0x76dc4190,0x4db26158,0xedb88320,0xd6d6a3e8,0x9b64c2b0,0xa00ae278};unsignedlongi,j,tap1,tap2,tap3,tap4,tap5;intinput_rotate;intwordmask=r->poolinfo->poolwords-1;constchar*bytes=in;__u32w;unsignedlongflags;/* Taps are constant, so we can load them without holding r->lock. */tap1=r->poolinfo->tap1;tap2=r->poolinfo->tap2;tap3=r->poolinfo->tap3;tap4=r->poolinfo->tap4;tap5=r->poolinfo->tap5;spin_lock_irqsave(&r->lock,flags);input_rotate=r->input_rotate;i=r->add_ptr;/* mix one byte at a time to simplify size handling and churn faster */while(nbytes--){w=rol32(*bytes++,input_rotate&31);i=(i-1)&wordmask;/* XOR in the various taps */w^=r->pool[i];w^=r->pool[(i+tap1)&wordmask];w^=r->pool[(i+tap2)&wordmask];w^=r->pool[(i+tap3)&wordmask];w^=r->pool[(i+tap4)&wordmask];w^=r->pool[(i+tap5)&wordmask];/* Mix the result back in with a twist */r->pool[i]=(w>>3)^twist_table[w&7];/* * Normally, we add 7 bits of rotation to the pool. * At the beginning of the pool, add an extra 7 bits * rotation, so that successive passes spread the * input bits across the pool evenly. */input_rotate+=i?7:14;}r->input_rotate=input_rotate;r->add_ptr=i;if(out)for(j=0;j<16;j++)((__u32*)out)[j]=r->pool[(i-j)&wordmask];spin_unlock_irqrestore(&r->lock,flags);}staticvoidmix_pool_bytes(structentropy_store*r,constvoid*in,intbytes){mix_pool_bytes_extract(r,in,bytes,NULL);}/* * Credit (or debit) the entropy store with n bits of entropy */staticvoidcredit_entropy_bits(structentropy_store*r,intnbits){unsignedlongflags;intentropy_count;if(!nbits)return;spin_lock_irqsave(&r->lock,flags);DEBUG_ENT("added %d entropy credits to %s\n",nbits,r->name);entropy_count=r->entropy_count;entropy_count+=nbits;if(entropy_count<0){DEBUG_ENT("negative entropy/overflow\n");entropy_count=0;}elseif(entropy_count>r->poolinfo->POOLBITS)entropy_count=r->poolinfo->POOLBITS;r->entropy_count=entropy_count;/* should we wake readers? */if(r==&input_pool&&entropy_count>=random_read_wakeup_thresh){wake_up_interruptible(&random_read_wait);kill_fasync(&fasync,SIGIO,POLL_IN);}spin_unlock_irqrestore(&r->lock,flags);}/********************************************************************* * * Entropy input management * *********************************************************************//* There is one of these per entropy source */structtimer_rand_state{cycles_tlast_time;longlast_delta,last_delta2;unsigneddont_count_entropy:1;};#ifndef CONFIG_GENERIC_HARDIRQSstaticstructtimer_rand_state*irq_timer_state[NR_IRQS];staticstructtimer_rand_state*get_timer_rand_state(unsignedintirq){returnirq_timer_state[irq];}staticvoidset_timer_rand_state(unsignedintirq,structtimer_rand_state*state){irq_timer_state[irq]=state;}#elsestaticstructtimer_rand_state*get_timer_rand_state(unsignedintirq){structirq_desc*desc;desc=irq_to_desc(irq);returndesc->timer_rand_state;}staticvoidset_timer_rand_state(unsignedintirq,structtimer_rand_state*state){structirq_desc*desc;desc=irq_to_desc(irq);desc->timer_rand_state=state;}#endifstaticstructtimer_rand_stateinput_timer_state;/* * This function adds entropy to the entropy "pool" by using timing * delays. It uses the timer_rand_state structure to make an estimate * of how many bits of entropy this call has added to the pool. * * The number "num" is also added to the pool - it should somehow describe * the type of event which just happened. This is currently 0-255 for * keyboard scan codes, and 256 upwards for interrupts. * */staticvoidadd_timer_randomness(structtimer_rand_state*state,unsignednum){struct{cycles_tcycles;longjiffies;unsignednum;}sample;longdelta,delta2,delta3;preempt_disable();/* if over the trickle threshold, use only 1 in 4096 samples */if(input_pool.entropy_count>trickle_thresh&&(__get_cpu_var(trickle_count)++&0xfff))gotoout;sample.jiffies=jiffies;sample.cycles=get_cycles();sample.num=num;mix_pool_bytes(&input_pool,&sample,sizeof(sample));/* * Calculate number of bits of randomness we probably added. * We take into account the first, second and third-order deltas * in order to make our estimate. */if(!state->dont_count_entropy){delta=sample.jiffies-state->last_time;state->last_time=sample.jiffies;delta2=delta-state->last_delta;state->last_delta=delta;delta3=delta2-state->last_delta2;state->last_delta2=delta2;if(delta<0)delta=-delta;if(delta2<0)delta2=-delta2;if(delta3<0)delta3=-delta3;if(delta>delta2)delta=delta2;if(delta>delta3)delta=delta3;/* * delta is now minimum absolute delta. * Round down by 1 bit on general principles, * and limit entropy entimate to 12 bits. */credit_entropy_bits(&input_pool,min_t(int,fls(delta>>1),11));}out:preempt_enable();}voidadd_input_randomness(unsignedinttype,unsignedintcode,unsignedintvalue){staticunsignedcharlast_value;/* ignore autorepeat and the like */if(value==last_value)return;DEBUG_ENT("input event\n");last_value=value;add_timer_randomness(&input_timer_state,(type<<4)^code^(code>>4)^value);}EXPORT_SYMBOL_GPL(add_input_randomness);voidadd_interrupt_randomness(intirq){structtimer_rand_state*state;state=get_timer_rand_state(irq);if(state==NULL)return;DEBUG_ENT("irq event %d\n",irq);add_timer_randomness(state,0x100+irq);}#ifdef CONFIG_BLOCKvoidadd_disk_randomness(structgendisk*disk){if(!disk||!disk->random)return;/* first major is 1, so we get >= 0x200 here */DEBUG_ENT("disk event %d:%d\n",MAJOR(disk_devt(disk)),MINOR(disk_devt(disk)));add_timer_randomness(disk->random,0x100+disk_devt(disk));}#endif#define EXTRACT_SIZE 10/********************************************************************* * * Entropy extraction routines * *********************************************************************/staticssize_textract_entropy(structentropy_store*r,void*buf,size_tnbytes,intmin,intrsvd);/* * This utility inline function is responsible for transfering entropy * from the primary pool to the secondary extraction pool. We make * sure we pull enough for a 'catastrophic reseed'. */staticvoidxfer_secondary_pool(structentropy_store*r,size_tnbytes){__u32tmp[OUTPUT_POOL_WORDS];if(r->pull&&r->entropy_count<nbytes*8&&r->entropy_count<r->poolinfo->POOLBITS){/* If we're limited, always leave two wakeup worth's BITS */intrsvd=r->limit?0:random_read_wakeup_thresh/4;intbytes=nbytes;/* pull at least as many as BYTES as wakeup BITS */bytes=max_t(int,bytes,random_read_wakeup_thresh/8);/* but never more than the buffer size */bytes=min_t(int,bytes,sizeof(tmp));DEBUG_ENT("going to reseed %s with %d bits ""(%d of %d requested)\n",r->name,bytes*8,nbytes*8,r->entropy_count);bytes=extract_entropy(r->pull,tmp,bytes,random_read_wakeup_thresh/8,rsvd);mix_pool_bytes(r,tmp,bytes);credit_entropy_bits(r,bytes*8);}}/* * These functions extracts randomness from the "entropy pool", and * returns it in a buffer. * * The min parameter specifies the minimum amount we can pull before * failing to avoid races that defeat catastrophic reseeding while the * reserved parameter indicates how much entropy we must leave in the * pool after each pull to avoid starving other readers. * * Note: extract_entropy() assumes that .poolwords is a multiple of 16 words. */staticsize_taccount(structentropy_store*r,size_tnbytes,intmin,intreserved){unsignedlongflags;/* Hold lock while accounting */spin_lock_irqsave(&r->lock,flags);BUG_ON(r->entropy_count>r->poolinfo->POOLBITS);DEBUG_ENT("trying to extract %d bits from %s\n",nbytes*8,r->name);/* Can we pull enough? */if(r->entropy_count/8<min+reserved){nbytes=0;}else{/* If limited, never pull more than available */if(r->limit&&nbytes+reserved>=r->entropy_count/8)nbytes=r->entropy_count/8-reserved;if(r->entropy_count/8>=nbytes+reserved)r->entropy_count-=nbytes*8;elser->entropy_count=reserved;if(r->entropy_count<random_write_wakeup_thresh){wake_up_interruptible(&random_write_wait);kill_fasync(&fasync,SIGIO,POLL_OUT);}}DEBUG_ENT("debiting %d entropy credits from %s%s\n",nbytes*8,r->name,r->limit?"":" (unlimited)");spin_unlock_irqrestore(&r->lock,flags);returnnbytes;}staticvoidextract_buf(structentropy_store*r,__u8*out){inti;__u32hash[5],workspace[SHA_WORKSPACE_WORDS];__u8extract[64];/* Generate a hash across the pool, 16 words (512 bits) at a time */sha_init(hash);for(i=0;i<r->poolinfo->poolwords;i+=16)sha_transform(hash,(__u8*)(r->pool+i),workspace);/* * We mix the hash back into the pool to prevent backtracking * attacks (where the attacker knows the state of the pool * plus the current outputs, and attempts to find previous * ouputs), unless the hash function can be inverted. By * mixing at least a SHA1 worth of hash data back, we make * brute-forcing the feedback as hard as brute-forcing the * hash. */mix_pool_bytes_extract(r,hash,sizeof(hash),extract);/* * To avoid duplicates, we atomically extract a portion of the * pool while mixing, and hash one final time. */sha_transform(hash,extract,workspace);memset(extract,0,sizeof(extract));memset(workspace,0,sizeof(workspace));/* * In case the hash function has some recognizable output * pattern, we fold it in half. Thus, we always feed back * twice as much data as we output. */hash[0]^=hash[3];hash[1]^=hash[4];hash[2]^=rol32(hash[2],16);memcpy(out,hash,EXTRACT_SIZE);memset(hash,0,sizeof(hash));}staticssize_textract_entropy(structentropy_store*r,void*buf,size_tnbytes,intmin,intreserved){ssize_tret=0,i;__u8tmp[EXTRACT_SIZE];unsignedlongflags;xfer_secondary_pool(r,nbytes);nbytes=account(r,nbytes,min,reserved);while(nbytes){extract_buf(r,tmp);if(r->last_data){spin_lock_irqsave(&r->lock,flags);if(!memcmp(tmp,r->last_data,EXTRACT_SIZE))panic("Hardware RNG duplicated output!\n");memcpy(r->last_data,tmp,EXTRACT_SIZE);spin_unlock_irqrestore(&r->lock,flags);}i=min_t(int,nbytes,EXTRACT_SIZE);memcpy(buf,tmp,i);nbytes-=i;buf+=i;ret+=i;}/* Wipe data just returned from memory */memset(tmp,0,sizeof(tmp));returnret;}staticssize_textract_entropy_user(structentropy_store*r,void__user*buf,size_tnbytes){ssize_tret=0,i;__u8tmp[EXTRACT_SIZE];xfer_secondary_pool(r,nbytes);nbytes=account(r,nbytes,0,0);while(nbytes){if(need_resched()){if(signal_pending(current)){if(ret==0)ret=-ERESTARTSYS;break;}schedule();}extract_buf(r,tmp);i=min_t(int,nbytes,EXTRACT_SIZE);if(copy_to_user(buf,tmp,i)){ret=-EFAULT;break;}nbytes-=i;buf+=i;ret+=i;}/* Wipe data just returned from memory */memset(tmp,0,sizeof(tmp));returnret;}/* * This function is the exported kernel interface. It returns some * number of good random numbers, suitable for seeding TCP sequence * numbers, etc. */voidget_random_bytes(void*buf,intnbytes){extract_entropy(&nonblocking_pool,buf,nbytes,0,0);}EXPORT_SYMBOL(get_random_bytes);/* * init_std_data - initialize pool with system data * * @r: pool to initialize * * This function clears the pool's entropy count and mixes some system * data into the pool to prepare it for use. The pool is not cleared * as that can only decrease the entropy in the pool. */staticvoidinit_std_data(structentropy_store*r){ktime_tnow;unsignedlongflags;spin_lock_irqsave(&r->lock,flags);r->entropy_count=0;spin_unlock_irqrestore(&r->lock,flags);now=ktime_get_real();mix_pool_bytes(r,&now,sizeof(now));mix_pool_bytes(r,utsname(),sizeof(*(utsname())));/* Enable continuous test in fips mode */if(fips_enabled)r->last_data=kmalloc(EXTRACT_SIZE,GFP_KERNEL);}staticintrand_initialize(void){init_std_data(&input_pool);init_std_data(&blocking_pool);init_std_data(&nonblocking_pool);return0;}module_init(rand_initialize);voidrand_initialize_irq(intirq){structtimer_rand_state*state;state=get_timer_rand_state(irq);if(state)return;/* * If kzalloc returns null, we just won't use that entropy * source. */state=kzalloc(sizeof(structtimer_rand_state),GFP_KERNEL);if(state)set_timer_rand_state(irq,state);}#ifdef CONFIG_BLOCKvoidrand_initialize_disk(structgendisk*disk){structtimer_rand_state*state;/* * If kzalloc returns null, we just won't use that entropy * source. */state=kzalloc(sizeof(structtimer_rand_state),GFP_KERNEL);if(state)disk->random=state;}#endifstaticssize_trandom_read(structfile*file,char__user*buf,size_tnbytes,loff_t*ppos){ssize_tn,retval=0,count=0;if(nbytes==0)return0;while(nbytes>0){n=nbytes;if(n>SEC_XFER_SIZE)n=SEC_XFER_SIZE;DEBUG_ENT("reading %d bits\n",n*8);n=extract_entropy_user(&blocking_pool,buf,n);DEBUG_ENT("read got %d bits (%d still needed)\n",n*8,(nbytes-n)*8);if(n==0){if(file->f_flags&O_NONBLOCK){retval=-EAGAIN;break;}DEBUG_ENT("sleeping?\n");wait_event_interruptible(random_read_wait,input_pool.entropy_count>=random_read_wakeup_thresh);DEBUG_ENT("awake\n");if(signal_pending(current)){retval=-ERESTARTSYS;break;}continue;}if(n<0){retval=n;break;}count+=n;buf+=n;nbytes-=n;break;/* This break makes the device work *//* like a named pipe */}/* * If we gave the user some bytes, update the access time. */if(count)file_accessed(file);return(count?count:retval);}staticssize_turandom_read(structfile*file,char__user*buf,size_tnbytes,loff_t*ppos){returnextract_entropy_user(&nonblocking_pool,buf,nbytes);}staticunsignedintrandom_poll(structfile*file,poll_table*wait){unsignedintmask;poll_wait(file,&random_read_wait,wait);poll_wait(file,&random_write_wait,wait);mask=0;if(input_pool.entropy_count>=random_read_wakeup_thresh)mask|=POLLIN|POLLRDNORM;if(input_pool.entropy_count<random_write_wakeup_thresh)mask|=POLLOUT|POLLWRNORM;returnmask;}staticintwrite_pool(structentropy_store*r,constchar__user*buffer,size_tcount){size_tbytes;__u32buf[16];constchar__user*p=buffer;while(count>0){bytes=min(count,sizeof(buf));if(copy_from_user(&buf,p,bytes))return-EFAULT;count-=bytes;p+=bytes;mix_pool_bytes(r,buf,bytes);cond_resched();}return0;}staticssize_trandom_write(structfile*file,constchar__user*buffer,size_tcount,loff_t*ppos){size_tret;structinode*inode=file->f_path.dentry->d_inode;ret=write_pool(&blocking_pool,buffer,count);if(ret)returnret;ret=write_pool(&nonblocking_pool,buffer,count);if(ret)returnret;inode->i_mtime=current_fs_time(inode->i_sb);mark_inode_dirty(inode);return(ssize_t)count;}staticlongrandom_ioctl(structfile*f,unsignedintcmd,unsignedlongarg){intsize,ent_count;int__user*p=(int__user*)arg;intretval;switch(cmd){caseRNDGETENTCNT:/* inherently racy, no point locking */if(put_user(input_pool.entropy_count,p))return-EFAULT;return0;caseRNDADDTOENTCNT:if(!capable(CAP_SYS_ADMIN))return-EPERM;if(get_user(ent_count,p))return-EFAULT;credit_entropy_bits(&input_pool,ent_count);return0;caseRNDADDENTROPY:if(!capable(CAP_SYS_ADMIN))return-EPERM;if(get_user(ent_count,p++))return-EFAULT;if(ent_count<0)return-EINVAL;if(get_user(size,p++))return-EFAULT;retval=write_pool(&input_pool,(constchar__user*)p,size);if(retval<0)returnretval;credit_entropy_bits(&input_pool,ent_count);return0;caseRNDZAPENTCNT:caseRNDCLEARPOOL:/* Clear the entropy pool counters. */if(!capable(CAP_SYS_ADMIN))return-EPERM;rand_initialize();return0;default:return-EINVAL;}}staticintrandom_fasync(intfd,structfile*filp,inton){returnfasync_helper(fd,filp,on,&fasync);}conststructfile_operationsrandom_fops={.read=random_read,.write=random_write,.poll=random_poll,.unlocked_ioctl=random_ioctl,.fasync=random_fasync,};conststructfile_operationsurandom_fops={.read=urandom_read,.write=random_write,.unlocked_ioctl=random_ioctl,.fasync=random_fasync,};/*************************************************************** * Random UUID interface * * Used here for a Boot ID, but can be useful for other kernel * drivers. ***************************************************************//* * Generate random UUID */voidgenerate_random_uuid(unsignedcharuuid_out[16]){get_random_bytes(uuid_out,16);/* Set UUID version to 4 --- truely random generation */uuid_out[6]=(uuid_out[6]&0x0F)|0x40;/* Set the UUID variant to DCE */uuid_out[8]=(uuid_out[8]&0x3F)|0x80;}EXPORT_SYMBOL(generate_random_uuid);/******************************************************************** * * Sysctl interface * ********************************************************************/#ifdef CONFIG_SYSCTL#include<linux/sysctl.h>staticintmin_read_thresh=8,min_write_thresh;staticintmax_read_thresh=INPUT_POOL_WORDS*32;staticintmax_write_thresh=INPUT_POOL_WORDS*32;staticcharsysctl_bootid[16];/* * These functions is used to return both the bootid UUID, and random * UUID. The difference is in whether table->data is NULL; if it is, * then a new UUID is generated and returned to the user. * * If the user accesses this via the proc interface, it will be returned * as an ASCII string in the standard UUID format. If accesses via the * sysctl system call, it is returned as 16 bytes of binary data. */staticintproc_do_uuid(ctl_table*table,intwrite,void__user*buffer,size_t*lenp,loff_t*ppos){ctl_tablefake_table;unsignedcharbuf[64],tmp_uuid[16],*uuid;uuid=table->data;if(!uuid){uuid=tmp_uuid;uuid[8]=0;}if(uuid[8]==0)generate_random_uuid(uuid);sprintf(buf,"%02x%02x%02x%02x-%02x%02x-%02x%02x-%02x%02x-""%02x%02x%02x%02x%02x%02x",uuid[0],uuid[1],uuid[2],uuid[3],uuid[4],uuid[5],uuid[6],uuid[7],uuid[8],uuid[9],uuid[10],uuid[11],uuid[12],uuid[13],uuid[14],uuid[15]);fake_table.data=buf;fake_table.maxlen=sizeof(buf);returnproc_dostring(&fake_table,write,buffer,lenp,ppos);}staticintuuid_strategy(ctl_table*table,void__user*oldval,size_t__user*oldlenp,void__user*newval,size_tnewlen){unsignedchartmp_uuid[16],*uuid;unsignedintlen;if(!oldval||!oldlenp)return1;uuid=table->data;if(!uuid){uuid=tmp_uuid;uuid[8]=0;}if(uuid[8]==0)generate_random_uuid(uuid);if(get_user(len,oldlenp))return-EFAULT;if(len){if(len>16)len=16;if(copy_to_user(oldval,uuid,len)||put_user(len,oldlenp))return-EFAULT;}return1;}staticintsysctl_poolsize=INPUT_POOL_WORDS*32;ctl_tablerandom_table[]={{.ctl_name=RANDOM_POOLSIZE,.procname="poolsize",.data=&sysctl_poolsize,.maxlen=sizeof(int),.mode=0444,.proc_handler=&proc_dointvec,},{.ctl_name=RANDOM_ENTROPY_COUNT,.procname="entropy_avail",.maxlen=sizeof(int),.mode=0444,.proc_handler=&proc_dointvec,.data=&input_pool.entropy_count,},{.ctl_name=RANDOM_READ_THRESH,.procname="read_wakeup_threshold",.data=&random_read_wakeup_thresh,.maxlen=sizeof(int),.mode=0644,.proc_handler=&proc_dointvec_minmax,.strategy=&sysctl_intvec,.extra1=&min_read_thresh,.extra2=&max_read_thresh,},{.ctl_name=RANDOM_WRITE_THRESH,.procname="write_wakeup_threshold",.data=&random_write_wakeup_thresh,.maxlen=sizeof(int),.mode=0644,.proc_handler=&proc_dointvec_minmax,.strategy=&sysctl_intvec,.extra1=&min_write_thresh,.extra2=&max_write_thresh,},{.ctl_name=RANDOM_BOOT_ID,.procname="boot_id",.data=&sysctl_bootid,.maxlen=16,.mode=0444,.proc_handler=&proc_do_uuid,.strategy=&uuid_strategy,},{.ctl_name=RANDOM_UUID,.procname="uuid",.maxlen=16,.mode=0444,.proc_handler=&proc_do_uuid,.strategy=&uuid_strategy,},{.ctl_name=0}};#endif /* CONFIG_SYSCTL *//******************************************************************** * * Random funtions for networking * ********************************************************************//* * TCP initial sequence number picking. This uses the random number * generator to pick an initial secret value. This value is hashed * along with the TCP endpoint information to provide a unique * starting point for each pair of TCP endpoints. This defeats * attacks which rely on guessing the initial TCP sequence number. * This algorithm was suggested by Steve Bellovin. * * Using a very strong hash was taking an appreciable amount of the total * TCP connection establishment time, so this is a weaker hash, * compensated for by changing the secret periodically. *//* F, G and H are basic MD4 functions: selection, majority, parity */#define F(x, y, z) ((z) ^ ((x) & ((y) ^ (z))))#define G(x, y, z) (((x) & (y)) + (((x) ^ (y)) & (z)))#define H(x, y, z) ((x) ^ (y) ^ (z))/* * The generic round function. The application is so specific that * we don't bother protecting all the arguments with parens, as is generally * good macro practice, in favor of extra legibility. * Rotation is separate from addition to prevent recomputation */#define ROUND(f, a, b, c, d, x, s) \ (a += f(b, c, d) + x, a = (a << s) | (a >> (32 - s)))#define K1 0#define K2 013240474631UL#define K3 015666365641UL#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)static__u32twothirdsMD4Transform(__u32constbuf[4],__u32constin[12]){__u32a=buf[0],b=buf[1],c=buf[2],d=buf[3];/* Round 1 */ROUND(F,a,b,c,d,in[0]+K1,3);ROUND(F,d,a,b,c,in[1]+K1,7);ROUND(F,c,d,a,b,in[2]+K1,11);ROUND(F,b,c,d,a,in[3]+K1,19);ROUND(F,a,b,c,d,in[4]+K1,3);ROUND(F,d,a,b,c,in[5]+K1,7);ROUND(F,c,d,a,b,in[6]+K1,11);ROUND(F,b,c,d,a,in[7]+K1,19);ROUND(F,a,b,c,d,in[8]+K1,3);ROUND(F,d,a,b,c,in[9]+K1,7);ROUND(F,c,d,a,b,in[10]+K1,11);ROUND(F,b,c,d,a,in[11]+K1,19);/* Round 2 */ROUND(G,a,b,c,d,in[1]+K2,3);ROUND(G,d,a,b,c,in[3]+K2,5);ROUND(G,c,d,a,b,in[5]+K2,9);ROUND(G,b,c,d,a,in[7]+K2,13);ROUND(G,a,b,c,d,in[9]+K2,3);ROUND(G,d,a,b,c,in[11]+K2,5);ROUND(G,c,d,a,b,in[0]+K2,9);ROUND(G,b,c,d,a,in[2]+K2,13);ROUND(G,a,b,c,d,in[4]+K2,3);ROUND(G,d,a,b,c,in[6]+K2,5);ROUND(G,c,d,a,b,in[8]+K2,9);ROUND(G,b,c,d,a,in[10]+K2,13);/* Round 3 */ROUND(H,a,b,c,d,in[3]+K3,3);ROUND(H,d,a,b,c,in[7]+K3,9);ROUND(H,c,d,a,b,in[11]+K3,11);ROUND(H,b,c,d,a,in[2]+K3,15);ROUND(H,a,b,c,d,in[6]+K3,3);ROUND(H,d,a,b,c,in[10]+K3,9);ROUND(H,c,d,a,b,in[1]+K3,11);ROUND(H,b,c,d,a,in[5]+K3,15);ROUND(H,a,b,c,d,in[9]+K3,3);ROUND(H,d,a,b,c,in[0]+K3,9);ROUND(H,c,d,a,b,in[4]+K3,11);ROUND(H,b,c,d,a,in[8]+K3,15);returnbuf[1]+b;/* "most hashed" word *//* Alternative: return sum of all words? */}#endif#undef ROUND#undef F#undef G#undef H#undef K1#undef K2#undef K3/* This should not be decreased so low that ISNs wrap too fast. */#define REKEY_INTERVAL (300 * HZ)/* * Bit layout of the tcp sequence numbers (before adding current time): * bit 24-31: increased after every key exchange * bit 0-23: hash(source,dest) * * The implementation is similar to the algorithm described * in the Appendix of RFC 1185, except that * - it uses a 1 MHz clock instead of a 250 kHz clock * - it performs a rekey every 5 minutes, which is equivalent * to a (source,dest) tulple dependent forward jump of the * clock by 0..2^(HASH_BITS+1) * * Thus the average ISN wraparound time is 68 minutes instead of * 4.55 hours. * * SMP cleanup and lock avoidance with poor man's RCU. * Manfred Spraul <manfred@colorfullife.com> * */#define COUNT_BITS 8#define COUNT_MASK ((1 << COUNT_BITS) - 1)#define HASH_BITS 24#define HASH_MASK ((1 << HASH_BITS) - 1)staticstructkeydata{__u32count;/* already shifted to the final position */__u32secret[12];}____cacheline_alignedip_keydata[2];staticunsignedintip_cnt;staticvoidrekey_seq_generator(structwork_struct*work);staticDECLARE_DELAYED_WORK(rekey_work,rekey_seq_generator);/* * Lock avoidance: * The ISN generation runs lockless - it's just a hash over random data. * State changes happen every 5 minutes when the random key is replaced. * Synchronization is performed by having two copies of the hash function * state and rekey_seq_generator always updates the inactive copy. * The copy is then activated by updating ip_cnt. * The implementation breaks down if someone blocks the thread * that processes SYN requests for more than 5 minutes. Should never * happen, and even if that happens only a not perfectly compliant * ISN is generated, nothing fatal. */staticvoidrekey_seq_generator(structwork_struct*work){structkeydata*keyptr=&ip_keydata[1^(ip_cnt&1)];get_random_bytes(keyptr->secret,sizeof(keyptr->secret));keyptr->count=(ip_cnt&COUNT_MASK)<<HASH_BITS;smp_wmb();ip_cnt++;schedule_delayed_work(&rekey_work,round_jiffies_relative(REKEY_INTERVAL));}staticinlinestructkeydata*get_keyptr(void){structkeydata*keyptr=&ip_keydata[ip_cnt&1];smp_rmb();returnkeyptr;}static__initintseqgen_init(void){rekey_seq_generator(NULL);return0;}late_initcall(seqgen_init);#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)__u32secure_tcpv6_sequence_number(__be32*saddr,__be32*daddr,__be16sport,__be16dport){__u32seq;__u32hash[12];structkeydata*keyptr=get_keyptr();/* The procedure is the same as for IPv4, but addresses are longer. * Thus we must use twothirdsMD4Transform. */memcpy(hash,saddr,16);hash[4]=((__forceu16)sport<<16)+(__forceu16)dport;memcpy(&hash[5],keyptr->secret,sizeof(__u32)*7);seq=twothirdsMD4Transform((const__u32*)daddr,hash)&HASH_MASK;seq+=keyptr->count;seq+=ktime_to_ns(ktime_get_real());returnseq;}EXPORT_SYMBOL(secure_tcpv6_sequence_number);#endif/* The code below is shamelessly stolen from secure_tcp_sequence_number(). * All blames to Andrey V. Savochkin <saw@msu.ru>. */__u32secure_ip_id(__be32daddr){structkeydata*keyptr;__u32hash[4];keyptr=get_keyptr();/* * Pick a unique starting offset for each IP destination. * The dest ip address is placed in the starting vector, * which is then hashed with random data. */hash[0]=(__force__u32)daddr;hash[1]=keyptr->secret[9];hash[2]=keyptr->secret[10];hash[3]=keyptr->secret[11];returnhalf_md4_transform(hash,keyptr->secret);}#ifdef CONFIG_INET__u32secure_tcp_sequence_number(__be32saddr,__be32daddr,__be16sport,__be16dport){__u32seq;__u32hash[4];structkeydata*keyptr=get_keyptr();/* * Pick a unique starting offset for each TCP connection endpoints * (saddr, daddr, sport, dport). * Note that the words are placed into the starting vector, which is * then mixed with a partial MD4 over random data. */hash[0]=(__forceu32)saddr;hash[1]=(__forceu32)daddr;hash[2]=((__forceu16)sport<<16)+(__forceu16)dport;hash[3]=keyptr->secret[11];seq=half_md4_transform(hash,keyptr->secret)&HASH_MASK;seq+=keyptr->count;/* * As close as possible to RFC 793, which * suggests using a 250 kHz clock. * Further reading shows this assumes 2 Mb/s networks. * For 10 Mb/s Ethernet, a 1 MHz clock is appropriate. * For 10 Gb/s Ethernet, a 1 GHz clock should be ok, but * we also need to limit the resolution so that the u32 seq * overlaps less than one time per MSL (2 minutes). * Choosing a clock of 64 ns period is OK. (period of 274 s) */seq+=ktime_to_ns(ktime_get_real())>>6;returnseq;}/* Generate secure starting point for ephemeral IPV4 transport port search */u32secure_ipv4_port_ephemeral(__be32saddr,__be32daddr,__be16dport){structkeydata*keyptr=get_keyptr();u32hash[4];/* * Pick a unique starting offset for each ephemeral port search * (saddr, daddr, dport) and 48bits of random data. */hash[0]=(__forceu32)saddr;hash[1]=(__forceu32)daddr;hash[2]=(__forceu32)dport^keyptr->secret[10];hash[3]=keyptr->secret[11];returnhalf_md4_transform(hash,keyptr->secret);}EXPORT_SYMBOL_GPL(secure_ipv4_port_ephemeral);#if defined(CONFIG_IPV6) || defined(CONFIG_IPV6_MODULE)u32secure_ipv6_port_ephemeral(const__be32*saddr,const__be32*daddr,__be16dport){structkeydata*keyptr=get_keyptr();u32hash[12];memcpy(hash,saddr,16);hash[4]=(__forceu32)dport;memcpy(&hash[5],keyptr->secret,sizeof(__u32)*7);returntwothirdsMD4Transform((const__u32*)daddr,hash);}#endif#if defined(CONFIG_IP_DCCP) || defined(CONFIG_IP_DCCP_MODULE)/* Similar to secure_tcp_sequence_number but generate a 48 bit value * bit's 32-47 increase every key exchange * 0-31 hash(source, dest) */u64secure_dccp_sequence_number(__be32saddr,__be32daddr,__be16sport,__be16dport){u64seq;__u32hash[4];structkeydata*keyptr=get_keyptr();hash[0]=(__forceu32)saddr;hash[1]=(__forceu32)daddr;hash[2]=((__forceu16)sport<<16)+(__forceu16)dport;hash[3]=keyptr->secret[11];seq=half_md4_transform(hash,keyptr->secret);seq|=((u64)keyptr->count)<<(32-HASH_BITS);seq+=ktime_to_ns(ktime_get_real());seq&=(1ull<<48)-1;returnseq;}EXPORT_SYMBOL(secure_dccp_sequence_number);#endif#endif /* CONFIG_INET *//* * Get a random word for internal kernel use only. Similar to urandom but * with the goal of minimal entropy pool depletion. As a result, the random * value is not cryptographically secure but for several uses the cost of * depleting entropy is too high */DEFINE_PER_CPU(__u32[4],get_random_int_hash);unsignedintget_random_int(void){structkeydata*keyptr;__u32*hash=get_cpu_var(get_random_int_hash);intret;keyptr=get_keyptr();hash[0]+=current->pid+jiffies+get_cycles();ret=half_md4_transform(hash,keyptr->secret);put_cpu_var(get_random_int_hash);returnret;}/* * randomize_range() returns a start address such that * * [...... <range> .....] * start end * * a <range> with size "len" starting at the return value is inside in the * area defined by [start, end], but is otherwise randomized. */unsignedlongrandomize_range(unsignedlongstart,unsignedlongend,unsignedlonglen){unsignedlongrange=end-len-start;if(end<=start+len)return0;returnPAGE_ALIGN(get_random_int()%range+start);}